Oblique coronal view through oral fissure on two‐dimensional grayscale and color Doppler ultrasound: diagnostic value for fetal cleft palate

Orofacial clefts comprise a range of congenital deformities, most commonly presenting as a cleft lip with or without a cleft palate (CLP) or an isolated cleft palate (CP). Prenatal ultrasound is the first-line diagnostic tool for identifying CLP, but its value in identifying CP so far has been limited. The palate is composed of bony and muscular segments that separate the oral and nasal cavities1. Owing to its dome-like structure, the palate cannot be entirely visualized on a single sonographic view. In 2010, Wilhelm and Borgers2 proposed that the ‘equals sign’, representing an intact soft palate detected by two-dimensional (2D) grayscale ultrasound, could rule out CP. This conclusion is based on the pathophysiological theory that CP always starts at the uvula and proceeds along the midline in the anterior direction, affecting either only the soft palate or both the soft and hard palates2. However, the disappearance of a typical equals sign only indicates clefts of the soft palate and does not further confirm the extent of CP. In order to improve the prenatal diagnosis of CP extending to the hard palate, we present a complementary 2D ultrasound approach, namely, the oblique coronal view through the oral fissure, combined with color Doppler of the fetal swallowing motion. First, the midsagittal view of the fetal face was obtained. Then, the probe was rotated 90°, and the transverse axial view at the level of the oral fissure was displayed. A subtle caudal tilt of the probe was followed, allowing the ultrasound beam to penetrate obliquely upwards through the oral fissure. Finally, an oblique coronal view through the oral fissure was achieved, in which both the oral and nasopharyngeal cavities, as well as the fetal hard palate in between was visualized. On the oblique coronal view using 2D ultrasound, an intact horizontal plate of palatine bone presented as a hyperechoic line (Figure 1), whereas the echo was seen to break when there was CP (Figure 2a). In addition, bidirectional color Doppler signals between the oral and nasopharyngeal cavities, which represents the amniotic fluid flow caused by the fetal swallowing motion, could be further observed using color Doppler flow imaging (Figure 2b). We consecutively diagnosed 12 cases of fetal CP (mean gestational age, 25 ± 2 weeks; range, 19–33 weeks) from October 2017 to May 2019. All cases displayed an absence of the ‘equals sign’ on 2D ultrasound examination, indicating the presence of a cleft of the soft palate. In the oblique coronal view through the oral fissure as described above, a cleft extending to the hard palate was further detected in all cases, which was confirmed by postnatal or postmortem examination. Owing to the small sample size, we were not able to conclude that this complementary approach has 100% accuracy for detecting clefts extending to the hard palate, which needs verification in future studies with a larger sample size. In conclusion, we have shown that 2D grayscale and color Doppler ultrasound features of the discontinuous hard palate on the oblique coronal view through the oral fissure are of incremental diagnostic value in fetal CP. We believe that the combination of the traditional view of the ‘equals sign’ and our proposed complementary 2D ultrasound approach will enable a more comprehensive assessment of CP on routine scans.